Download CHAPTER 12—STELLAR EVOLUTION

CHAPTER 12—STELLAR EVOLUTION
Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
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1. The main sequence has a limit at the lower end because
a. low mass stars form from the interstellar medium very rarely.
b. hydrogen fusion combined 4 hydrogen nuclei to form 1 helium nucleus.
c. pressure does not depend on temperature in degenerate matter.
d. the lower limit represents when the radius of the star would be zero.
e. there is a minimum temperature for hydrogen fusion.
2. There is a mass-luminosity relation because
a. hydrogen fusion produces helium.
b. stars expand when they become giants.
c. stars support their weight by making energy.
d. the helium flash occurs in degenerate matter.
e. all stars on the main sequence have about the same radius.
3. As a star like the sun exhausts hydrogen in its core, the outer layers of the star
a. become hotter and more luminous.
b. become cooler and more luminous.
c. become hotter and less luminous.
d. become cooler and less luminous.
e. become larger in radius and hotter.
4. Helium fusion is called the triple alpha process because
a. the helium nucleus is known as an alpha particle.
b. it occurs very rapidly.
c. it requires a temperature three times greater than that of hydrogen fusion.
d. it is the third source of the primary fusion processes.
e. each reaction produces three carbon nuclei.
5. A star will experience a helium flash if
a. it is more massive than about 6 solar masses.
b. its core contains oxygen and helium.
c. its mass on the main sequence was less than 0.1 solar masses.
d. it is a supergiant.
e. its core is degenerate when helium ignites.
6. In degenerate matter
a. pressure depends only on the temperature.
b. temperature depends only on density.
c. pressure does not depend on temperature.
d. pressure does not depend on density.
e. b and c
7. Giant and supergiant stars are rare because
a. they do not form as often as main sequence stars.
b. the giant and supergiant stage is unstable.
c. the giant and supergiant stage is very short.
d. helium is very rare.
e. helium flash destroys many of the stars before they can become giants and supergiants.
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8. Variables of a certain type are called Cepheid variable because
a. the first one discovered was in the constellation of Cepheus.
b. they were discovered by Anna Marie Cepheid and her brother Raul.
c. they all lie in the Cepheus star cluster.
d. they can be used to determine the distance to Cepheid star clusters.
e. they can be used to determine the distance to all of the stars in the Cepheid galaxy.
____ 9. When the Cepheid variable RU Camelopardalis stopped pulsating, astronomers speculated that it was
a. exhausting its helium.
b. exhausting its hydrogen.
c. turning off its triple alpha process.
d. evolving out of the instability strip.
e. becoming a red supergiant.
____ 10. A young star cluster will have _______________ than an older star cluster.
a. a redder turn-off point
b. a bluer turn-off point
c. fewer stars
d. fewer luminous stars
e. more low mass stars
____ 11. What is the approximate age of the star cluster in the diagram below?
a. 2 million years
b. 2 billion years
c. 10 billion years
d. 100 billion years
e. The age of the cluster can not be estimated from an HR diagram of the cluster.
____ 12. Open clusters tend to be _______________ than globular clusters.
a. younger and contain fewer stars
b. younger and contain more stars
c. older and contain fewer stars.
d. older and contain more stars.
e. more luminous and cooler
____ 13. Star cluster are important to our study of stars because
a. all stars formed in star clusters.
b. the sun was once a member of a globular cluster.
c. they give us a method to test the our theories and models of stellar evolution.
d. they are the only objects that contain Cepheid variables.
e. all of the above
____ 14. The triple alpha process
a. controls the pulsations in Cepheid variable stars.
b. is the nuclear fusion of hydrogen to helium in massive stars.
c. is the process that produces the neutrinos we receive from the sun.
d. requires a temperature of about 5,000,000 K to operate
e. occurs during helium flash.
____ 15. A star in the instability strip pulsates because
a. the energy produced by the core is not constant.
b. the energy produced by the hydrogen burning shell is not constant.
c. the core of the star is composed of helium and degenerate electrons.
d. the surface temperature of the star is increasing.
e. density and opacity of the helium ionization zone changes with time.
____ 16. The lowest mass object that can initiate thermonuclear fusion of hydrogen has a mass of about
a. 1 M .
b. 60 M .
c. 0.5 M .
d. 0.08 M .
e. 0.001 M .
____ 17. Which of the following nuclear fuels does a one solar mass star use over the course of its entire evolution?
a. hydrogen
b. hydrogen and helium
c. hydrogen, helium and carbon
d. hydrogen, helium, carbon, and neon
e. hydrogen, helium, carbon, neon, and oxygen.
____ 18. Which of the following nuclear fuels does a 0.2 solar mass star use over the course of its entire evolution?
a. hydrogen
b. hydrogen and helium
c. hydrogen, helium and carbon
d. hydrogen, helium, carbon, and neon
e. hydrogen, helium, carbon, neon, and oxygen.
____ 19. Helium flash occurs
a. because helium is very explosive and cannot be controlled when the nuclear reactions
occur.
b. because degenerate electrons in the core do not allow the core to expand as it heats up.
c. in Cepheid variables.
d. in stars with masses less than 0.4 M .
e. none of the above
____ 20. A Cepheid variable with a mass of 10 M _______________ than a Cepheid of 3 M .
a. is less luminous
b. has a greater surface temperature
c. has a smaller radius
d. has a longer period
e. a and c
____ 21. RR Lyrae variables
a. are less luminous than Cepheid variables.
b. have longer periods than Cepheid variables.
c. do not have a period-luminosity relationship.
____ 22.
____ 23.
____ 24.
____ 25.
d. are eclipsing variables.
e. a and b
The changing period of a Cepheid variable tells us that the
a. star's luminosity is increasing.
b. surface temperature of the star is increasing.
c. hydrogen burning core has quit burning its nuclear fuel.
d. star is evolving.
e. star is about to undergo helium flash.
It is assumed that stars in a star cluster
a. all have the same age.
b. all have the same chemical composition.
c. all have the same luminosity.
d. all of the above
e. a and b above
If the stars at the turnoff point of a cluster have a mass of 3 M , what is the age of the cluster?
a. 3.0 1010 years
b. 3.3 109 years
c. 6.4 108 years
d. 1.6 1011 years
e. The age of a star cluster can not be determined from the mass of stars at the turnoff point.
In the diagram below, which point indicates the location on the HR diagram of a one solar mass star when it
undergoes helium flash?
a. 1
b. 2
c. 3
d. 4
e. 5
____ 26. What is the lifetime of a 10 M star on the main sequence?
a. 3.2 107 years
b. 320 years
c. 3.2 1012 years
d. 1 109 years
e. 1 1011 years
True/False
Indicate whether the sentence or statement is true or false.
____ 27. Stars support their weight by generating energy in their centers.
____ 28. Stars swell into giants when hydrogen is exhausted in their centers.
____ 29. The helium flash is the cause of some supernovae.
____ 30. Helium fusion does not begin until the star has entered the giant region of the H-R diagram.
____ 31. Even in degenerate matter, pressure depends on temperature.
____ 32. Giant and supergiant stars are rare because that stage is short.
____ 33. Of the stars in the instability strip, the more massive stars have longer periods and lower luminosities.
____ 34. Cepheid variables can be used to determine distances because their absolute magnitude can be determined
from their period.
____ 35. Young star clusters have bluer turn-off points than old clusters.
____ 36. Even the youngest star clusters have no stars still contracting toward the main sequence.
CHAPTER 12
Answer Section
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